Pseudomonas viridiflava: An internal outsider of the Pseudomonas syringae species complex

Authors: LIPPS, SAVANA - University Of Minnesota; Samac, Deborah - Debby

Submitted to: Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2021
Publication Date: 8/31/2021
Citation: Lipps, S.M., Samac, D.A. 2021. Pseudomonas viridiflava: An internal outsider of the Pseudomonas syringae species complex. Molecular Plant Pathology. 23(1):3-15. https://doi.org/10.1111/mpp.13133.
DOI: https://doi.org/10.1111/mpp.13133

Interpretive Summary: Pseudomonas viridiflava, is a bacterial plant pathogen that has recently come under scrutiny due to the increasing occurrence of serious disease epidemics on a wide range of host plants. It is part of the pathogen complex causing bacterial blight of alfalfa. We identify the genes and mechanisms used by P. viridiflava to cause disease, which suggest that P. viridiflava is distinct from closely related bacteria P. syringae. Defining the characteristics of P. viridiflava is important for development of disease resistant plants and disease management practices. Effective disease management is needed for maintaining alfalfa herbage yields and plant persistence to reduce economic risks for farmers.

Technical Abstract: Pseudomonas viridiflava is a Gram-negative Pseudomonad associated with the Pseudomonas syringae species complex. P. viridiflava has a wide host range and causes a variety of symptoms in different plant parts including stems, leaves, and blossoms. Outside of its pathogenic niche, P. viridiflava also exists as an endophyte, epiphyte, and saprophyte. Increased reports of P. viridiflava causing disease on new hosts in recent years coincide with increased research on genetic variability, virulence, phylogenetics, and phenotypes of this pathogen. This species is genetically and phenotypically diverse- there is a high level of variation in the core genome, virulence factors, and phenotypic characteristics. The main virulence factors of this pathogen include the enzyme pectate lyase as well as virulence genes encoded within one or two pathogenicity islands. The delineation of P. viridiflava in the P. syringae complex has been investigated using several molecular approaches. P. viridiflava comprises its own species, or genomospecies, within the P. syringae complex. While seemingly an outsider to the complex as a whole because of differences in the core genome and virulence genes, low average nucleotide identity to the majority of P. syringae complex members, and some phenotypic traits, it remains as part of the complex. Defining the phylogenetic, phenotypic, and genomic characteristics of P. viridiflava in comparison to other P. syringae members is important to understanding this pathogen and development of disease resistant plants and management practices in the future.